Transcript Novel RFI Measurement

High Voltage Substation Surveillance using Radio Frequency
Interference Measurement
Detecting partial discharge
(indirect measurement)
RFI
Electric
Thermal
Partial
discharge
Pressure/
Acoustic
Acoustic
Light
Chemical
RF pulse from a PD related source
Partial discharge pulse
RFI emission
FFT frequency spectrum of
PD pulse
5
CASE Inkoo 110 kV CT
• Selective testing targeting mainly
old 110 kV CTs discovered a unit
with a high C2 power factor ~0,95
%. (Strömberg KOTU F41 type,
manuf. 1972)
• A DGA follow up showed
considerable gassing TCG 18 000
ppm (H2 12037 ppm, CH4 4839
ppm, C2H6 1058 ppm) diagnosed
as D1 low energy discharge
• Suitable test case...?
• Doble were asked for a PDS100
blind test.
6
Pvm
Esityksen nimi / Tekijä
7
Baseline measurement
Baseline measured outside the fences
Low backround noise levels
0
-10
Tr166-110 kV Baseline
-20
-30
Discharges in oil will have
higher frequency content
dB
-40
-50
-60
-70
GSM
Typical frequency zone for air
discharges <150 MHz
-80
-90
50
145
240
335
430
525
MHz
620
715
810
905
1000
8
No signals
0
Tr166-Baseline
Tr171
-10
-20
-30
-40
-50
-60
-70
50
145
240
335
430
525
620
715
810
905
1000
0
-10
Tr166 Baseline
Tr170
-20
-30
-40
Baseline
-50
-60
-70
50
-60
-60
-70
-70
50
145
240
335
430
525
MHz
620
715
810
905
1000
810
905
1000
TR168 Phase R
-30
dB
dB
-50
715
-20
-40
-50
620
Baseline
-30
-40
525
-10
-20
-30
430
Tr169 - Phase T
-10
-10
-20
335
0
Baseline
Baseline
Tr167
240
Suspected item
0
0
145
-40
-50
-60
50
145
240
335
430
525
MHz
620
715
810
905
1000
-70
50
145
240
335
430
525
Measuring points on the service road between CBs and CTs
620
715
810
905
1000
9
Measurements
The faulty unit was succesfully located
– A small PD signal was registered ~15dB
above baseline
– Attennuation of high frequencies is useful in
the location process
– The 110 kV CT was replaced - no signal
after replacement (one month later)
10
HV Lab testing of the CT
• PD Ignites at 74 kV phase-to-earth voltage (128 kV main voltage),
apparent charge was 50-60 pC
• Extinguishing voltage is considerably lower around 45 kV (77 kV
main voltage)
• At 1,2 x Um/ (85 kV) discharge level was 150 pC
• Internal pressure 0,75 bar (0,6 considered normal)
• Tandelta slightly increasing as a function of voltage up to 70 kV,
0,43...0,59 %
• Tandelta increases rapidly when PD ignites at 74 kV being 1,76 %
at 123 kV
• CT passed the 0,75 x 230 kV, 50 Hz 1 min overvoltage test
Advantages of RFI
• Non-invasive, no need for
physical or electrical
connection.
• Does not require
equipment under test to
be taken out of service.
• May be adopted for firstline substation
surveillance.
• Rate and severity of
discharge can be
monitored and trended.
Thanks for your kind attention!
Questions?
Contact:
Alan Nesbitt
Brian Stewart
Glasgow Caledonian
University
Scotland, UK
[email protected]
Contact:
Micael Hellquist
Hans Ove Kristiansen
Doble TransiNor AS
Norway
[email protected]